This invention relates to a beam shaping device for shaping the cross section of a light beam comprising at least one beam shaping unit with beam division means, beam deflection means and beam combination means, the beam division means being able to divide a light beam incident on the beam shaping unit into two component beams, the beam deflection means being able to deflect at least one of the component beams to the beam combination means, and the beam combination means being able to combine the two component beams, such that the cross section of the light beam emerging from the beam shaping unit compared to the cross section of the light beam entering the beam shaping unit is reduced in the first direction and is enlarged in a second direction which is perpendicular to it. Furthermore, this invention relates to an arrangement for injecting a light beam with an elongated cross section proceeding from an elongated laser light source into an optical fiber, comprising a laser light source, a collimation unit which is located behind it in the beam direction, a beam shaping device of the aforementioned type and a focussing unit which is located behind the beam shaping device and which can focus the beam incident on it onto the optical fiber.
A beam shaping device of the aforementioned type and an arrangement of the aforementioned type are known from German patent DE 195 37 265 C1. In the embodiment of a beam shaping unit described in it a rhomboid prism pair which separates the incident radiation into two component beam bundles is used as the beam division means. The beam deflection means are two half cubic prisms which are integrated into the corresponding component beam paths, as a result of the relatively long path of the component beam bundle which has been traversed in this beam shaping unit there being a lens located between the rhomboid prism pair and the half cube prism. The beam combination means is a fifth prism which deflects the component beam bundles which are incident on it and combines them again.
The disadvantage in this beam shaping unit is that overall seven components are used, each of the individual component beams passing through eight optionally partially absorbing surfaces of optical components and being reflected each on two other surfaces of the aforementioned components, which surfaces may not be 100% reflective. Based on the many surfaces which must be transmitted or on which reflection must take place, a relatively great cost must be borne to coat the surfaces accordingly with respect to transmission or reflection. In particular, when several of these beam shaping units are set up in succession, such a beam shaping device will be less effective. Furthermore, as a result of the many components used and as a result of the high coating cost these beam shaping units will be extremely expensive.
An arrangement of the initially mentioned type is generally used whenever for example laser radiation proceeding for example from a laser diode bar is to be focussed on an optical fiber. In particular, as a result of the almost line-shaped laser light source with individual emission centers which are located spaced apart over the length of the line and the different divergences in the slow axis and fast axis direction, it is a good idea to use a beam shaping device of the initially mentioned type in order to repeatedly shape and combine the laser light emerging from the laser diode bar with an almost line-shaped cross section, so that a laser beam bundle with an almost square cross section is formed which then can be focussed more easily on the optical fiber. The effectiveness and economic efficiency of such an arrangement of course follow from the effectiveness and economic efficiency of the beam shaping device used in it.
One object of this invention is to devise a beam shaping device of the initially mentioned type and an arrangement of the initially mentioned type which are built efficiently and economically.
The beam combination means are also used as beam division means, only one of the component beams being deflected by the beam deflection means, conversely the other component beam being directly incident on the beam combination means. This measure drastically reduces the number of transmissions or reflections of the individual component beams. Furthermore, a beam shaping unit as claimed in the invention in the ideal case can consist of two individual optical components, conversely in the prior art for the same function seven components being necessary. In particular, one of the component beams will be incident directly on the beam combination means without prior passage through other optical components so that for this component beam the number of transmissions or reflections is minimized. Advantageously the second of the component beams for dividing the beam will run unhindered past the component which is being used as the beam combination means and the beam division means and will be deflected by the beam deflection means onto the functional sections of the component which is used as the beam combination means and the beam division means, which sections are used as beam combination means. This measure also minimizes the number of transmissions and reflections of the second component beam.
Advantageously the beam combination means comprise two specular surfaces which include an angle to one another, and each of the component beams which are to be combined by the beam combination means can be reflected on one of the specular surfaces. Especially for the case in which the specular surfaces are the outside surfaces of the beam combination means, each of the component beams will undergo only one reflection on this component, but not an additional transmission.
According to one preferred embodiment of this invention, there is a single prism as the beam combination means and at the same time the beam division means, the specular surfaces which reflect the component beams being made as preferably mirrored surfaces of this prism. Such a prism represents an especially simple but nevertheless very effective embodiment of the component which is used at the same time as the beam combination means and beam division means.
Advantageously the prism which is used as the beam division means and as the beam combination means can have a base surface which is made as an isosceles right triangle, the specular surfaces being those prism surfaces which each extend between the legs of the base surfaces so that the specular surfaces include an angle of 90xc2x0 with one another. By choosing one such right-angled prism the desired beam combination function can be implemented most easily, in which specifically the two specular surfaces which are at an angle of 90xc2x0 to one another are each aligned at an angle of 45xc2x0 or xe2x88x9245xc2x0 to the component beams which run from the opposite directions onto the prism.
Here the prism which is used as the beam division means or as the beam combination means can be located in the beam shaping unit such that the light beam which is incident on the beam shaping unit and which is to be shaped is cut in half in the first direction which is essentially perpendicular to the direction of propagation of the light beam, such that one of the two component beams which is formed by this halving runs past the prism onto the beam deflection means and the other of the two component beams which is formed by this halving is directly incident on the first of the two specular surfaces and is reflected by them in the direction of the light beam leaving the beam shaping unit. By this cutting of the beams in half on the prism the first of the two component beams in the entire beam shaping unit will ultimately undergo only one reflection on the first of the two specular surfaces and not transmission. The other of the component beams according to the choice of the beam deflection means will undergo two to four reflections or transmissions on the beam deflection means and exactly one reflection on the second specular surface, but an additional transmission neither on the beam division means nor on the beam combination means. In this way the number of transmissions and reflections is minimized with a simultaneous extremely economical structure of the beam shaping device as claimed in the invention.
Preferably the prism which is used as the beam division means or as the beam combination means is located in the beam shaping unit such that a light beam which is incident on the beam shaping unit runs parallel to the prism surface which connects to one another the two prism surfaces which are made as specular surfaces. This ensures that with the corresponding calibration of the light beam which is to be shaped exactly one half of the beam is incident on the first mirror surface and the other half of the beam runs past the prism in the direction to the beam deflection means and now parts of the beam are not absorbed or reflected away in an uncontrolled manner on any additional edges or the like.
Here it can be provided that the component beam which runs past the prism which is being used as the beam division means or beam combination means is incident on the beam deflection means in the propagation direction behind the prism; the beam deflection means deflect the component beam such that it is incident on the second of the specular surfaces in the direction which is opposite the propagation direction and is reflected by these surfaces in the direction of the light beam which is leaving the beam shaping unit. In this way the structure of the beam shaping device or beam shaping unit as claimed in the invention is relatively compact.
According to one preferred embodiment of this invention, the beam deflection means are made as an imaging unit and cause 1:1 imaging of the component beam which is incident on it onto the second specular surface. This imaging results in that the two component beams can be optimally combined by the beam combination means because especially no divergence or hardly any different divergence can occur between the two component beams.
Preferably the imaging unit here can have essentially the shape of a planoconvex lens, and the component beam can enter the imaging unit through the convex lens surfaces, can be reflected on the plane surface which is preferably mirrored and can emerge from the convex lens surface in the direction to the second specular surface of the beam combination means. In this way deflection and the associated 1:1 imaging is accomplished by two transmissions and one reflection so that overall very effective shaping of the beam cross section occurs.
According to another embodiment of this invention, the beam deflection means is made as a prism, and the component beam which is incident on the prism can be deflected by it in the direction which is opposite the propagation direction onto the second specular surface of the beam combination means. The choice of a prism as the beam deflection means is an especially good idea for very extended beam cross sections because by inserting a prism into the beam path no additional imaging errors can occur, as would be the case in a lens or the like.
Here the prism which is used as a deflection means can likewise have a base surface which is made as an isosceles right triangle, the component beam entering the prism passing vertically through the prism surface which connects the base sides of these triangles to one another and on each of the other two prism surfaces being reflected at an angle of essentially 45xc2x0, preferably the two prism surfaces on which the component beam is reflected being mirrored. A beam deflection means which is made in this way is characterized by an extremely simple and economical structure with high functionality.
Advantageously, the beam shaping device can have more than one beam shaping unit, especially three or four beam shaping units which are arranged in succession such that the cross section of the light beam is made smaller in each of the beam shaping units in the first direction and is enlarged in the second direction which is perpendicular to it. Here the cross section of the light beam emerging from the beam shaping unit or from one of the beam shaping units compared to the cross section of the light beam entering the beam shaping unit or one of the beam shaping units can be cut in half in the first direction and can be doubled in the second direction which is perpendicular to it. For example, by connecting four such beam shaping units in succession the light beam would be compressed by a factor of 16 in the first direction and in the second direction perpendicular to it pulled apart by a factor of 16. Thus such a beam shaping unit is especially suited for the initially mentioned arrangement for injecting of the laser beam emerging for example from a laser diode bar into an optical fiber.